Can't create a specific displacement based on voronoi texture
To save too much strain on the GPU, you may want to separate the business of displacing faces and coloring them, to give the renderer some geometry to work with in the cracks.
You could make a displacement map based on Distance From Edge, shown on the left, below, and a sparate parallel Voronoi to color the displaced faces.

This is a 2D Voronoi, mapped to the surface of the sphere as described here, but the principle would be the same for other cell-like textures